Amine absorbent gas treating system



Aug- 26, 1952 H. D. FRAzlER ET AL 2,608,462

AMINE ABSORBENT GAS TREATING SYSTEM Filed March 26, 1949 @En C JQ/ESENFE/.Q

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Patented Aug. 26, 1952 AMINE ABSORBENT GAS TREATING SYSTEM Henry D. Frazier, Alhambra, and Fred C. Riesenfeld, Hollywood, Calif., assignors to The `Fluor Corporation, Ltd., Los Angeles, Calif., a` corpo-i` ration of California Application March 2s, 1949, seriaiNo. 83,740

. This invention has to do with advances and improvements in processes for treating gaseous mixtures by contact with liquid amine solutions, to remove from the gas one or more acidic impurities. Particularly the invention is directed *to the treatment of hydrocarbon natural or renery gases containing such acidicimpurities as carbon dioxide and hydrogen sulfide, primarily `for the purpose of removing the hydrogen sulfide.

It iscustomary practice to pass the gaseous mixture through and in intimate contact with an amine solution circulated through a contacting zone from which the rich solution is regenerated in a heating zone and then returned to the gas contacting stage. The conventional contactor consists of a multiple tray column through which the gas ows upwardly andcountercurrently to the down-flowing` amine solution introduced onto a top tray of the treating section. Ordinarily substantially all the hydrogen sulde in the gasbeing treated will be absorbed in the amine solution, and most if not virtually, all of the carbon dioxide content of the gas will similarly be absorbed." The capacity of the solution for acid gas absorption, as well as dehydration of the gas when desirable, is favored by the use of glycol-amine solutions of the character dealt r with in Hutchinson Patent Number 2,177,068.

Invproper contactor'column operation, a close .9

approach to equilibrium relationship 'exists on Vthe top contactor section tray between the components oi the leaving gas stream and the lean amine solution. And by virtue of Vthat relationship, some of the amine will be carried inthe treated gas stream. We refer to such amine as being entrained in the gas, and in so doing, include both liquid and vaporized amine that may be carried by the gas iiowing beyond its contact withthe lean amine solution. Generally, the treated gas may contain little if any carbon dioxide, for the reason that while its presence, as contrasted with anysubstantial hydrogen suliide content, may beunobjectionable in the treated gas, the maintenance of such conditions of contactor operation as will permit passage of considerable quantities of carbon dioxide, ordinarily would allow an objectionable residue of hydrogen Y.sulfide in the treated gas. Consequently the carbon dioxide 'concentration in the treated gas stream is `insufficient to eiiect the amine conversion discussed in the following.

Considering now another aspect of the contactor operation, it is desirable for highest treating eiciency that. maximum intimacy or con- 9 claims.` (ci. ca -2) tact be had between 2 i 1 "y the gas and aminesolution, and accordingly, that the amine have? the "lowest permissible viscosity consistent with high basicity.` Heretofore, an undesirable limitation has existed, relative to the use `ofj the lower molecular weight and less 'viscous amines, due to the fact that their higher vapor pressures necessarily entailhigh vaporization losses at the top tray under the equilibrium conditions referred to above. Accordingly the useable amines have been selected to best compromise molecular weight and vapor pressure conditions.

The invention basin common with thefdevelopments disclosed in eopending appllcations of Frazier, Ser. No.f83,738, 'entitled Prevention of Amine Losses in Gas? Treating Systems, J "and Frazier and Kohl; Ser. No. 83,739, entitledystems for theTreatment of Gases,.the general'ob- `jective of reacting the `amine entrained in the treated gas stream, with anacidic compound Ato convert the amine to a relatively high molecular weight compound of such low vapor pressure as tobe readily separable and recoverable from the gas. The present invention is particularly directed to amethod whereby the amine solution circulated in the plant treating cycle is 1 `employed as a carrier for the acidic compound to `be reacted with the entrained amine, `all in a system of continuous operation whereby the amine solution finally to contact the gas has such acidic content or concentration as will maintain the amine constituency of the solution itself, as well as any amine entrainment contacting the solution, inthe form of a reaction productreturnable to the treating amine cycle for regeneration and having such low vapor pressure as to resist consequential entrainment in the gas stream. Since, accordingly, the resistance of the amine to entrainment in the finally `treated gas is in eiect governed by the molecular weight and vapor pressure characteristics of the amine-acidic compound reaction 'product rather than the composition of the amine as which the aminoradical is attached to arycarbon aliphatic or straight chain groups, saturated or unsaturated, or to a saturated or unsaturated ring structure. The preferred amines are those of low viscosity, and having a Vapor pressure at least as high as the Vapor pressure of monoethanolamine. The less Viscous and higher vapor pressure amines include amines of lower moleculanweight and higher vapor pressure than vmonoethanolamine, typically methylamine, ethylene diamino, the normally liquid alkylene polyamines, normally liquid alkylamines whose Y .der physotbabsorption therein, the :aminecarry- ":overzgfromvthe vtreating stage -is .effectively :trapped: .fisV will appear, provi-sionfisfmadef.for'

,-feontinuous regeneration of a-portion of` the, car- :sbamatestream by' return to the amine ysolution l undergoing regeneration-in .the still.

y .Various addi-tional tfeatures and-objects of the A ventigon as well-'as the vdetails of a.-typical.em v,ebodinentzthereof, will beaunderstood to better advantage-:from-the fol-lowing detailed descripztionjpthe accompanying drawing,-y Whic-h illus- .;.:trates..the processV in iiowv sheet r-form.

' vRefer-ring :tothe drawing, the gas treating sys-v '1r,-.tem1imay,be taken typically to comprise a usual Nfifcontaeter :column IIIy ytothe hasey ofwhich'isyied i throughY 1ine:.-I,|rth e gaseousmixture to be treated, fzs-.andi consisting typically of a hydrocarbon nat- Iliuralzor: refinery gas; containing such acidic -im- .ipuritieslas ,eitherwor bothzcarbon ,dioxide and @hydrogen sulfide. aThe gas lpasses 4upwardly -'througlfi Ythe column counter-currently to a down umlowing streamiof. lean amine. solution-introduced ci' straight. .amine-@absorbent containing-from 110 to r l5%faliphatic. amine (e. .gli monoet-hanolamine) e water; for; a. combination glycol-.amine soluzztionacomposed'rsayfof from 150` 110.80% glycol,4 `40 151%:amine,'and5 to 20% water. i .-'lheL rich amine.solutionremoyedxfromthe; con- A itactorfichimneyc trayV 'I 3,` is discharged through dine-.f Ifduandexchangeri.I51to the stillcolumn I6 :wherein the richsolution is subjected to heating f and7;regenerati'on..v `^Moisture3andacidgases leav -zing :the-i: stillgthroughline "If'I iare xcooledin Ioon- 'rdenseri I ligand water condensate collecting ingaatcumulatorel;is/returnedgas reflux to,. the still f-fcolumnybypump-120'A through line A2|. The -un- :.cQndensedgasesleave the systemthrough line t2-2;.1f,1-Ieatf-i sf supplied tothe base of the stillcolwumnfas by; the usual 'reboilerfgenerallyV indicated at .,23. From v,the still: the. lean absorbent.- passes throughE line -24,exchanger :I5 ltoythe pumpi25, -,-fand.fisdischarged through: line I'2fand1cooler-26 tofthe-eontactor column I IJ.V A portion `of .the lean solution `being-returned .to ..the. contacter through line. I2y flows..to the top of a saturator. column .28.throug-h line 29,under ...control .of valve .ioperated by theconventionally f. indicated... regulator .3,lI .in accordance with f the wtliquid level in the .saturator Y. An acid -gas corh.@respondng .to an. acidic constituent vof .the ses mixture fed to the lsystem.,through line I I and .igconsisting preferably j of carbon.. dioxdafis .in-

'4 troduced to the base of the saturator through line 32. In flowing upwardly within the saturator, the carbon dioxide is absorbed in the downflowing amine solution, the quantity of carbon dioxide thus introduced preferably being sufcient to completely saturate the amine solution. The degree .of saturationmaybexsuchathat additional carbon dioxidebecomes dissolved or carried as such in the liquid amine solution.

In the saturator 28, the amine is converted by reaction with the carbon dioxide gas, to the relativelyhigh molecular weight carbamate which,

by reason of: itsrlow vapor pressure, may be emv-ployed :asfacarrier for carbon dioxide tol be reactedxwithamine entrained in the gas'stream cafter; its :removal from the lean solution in the ment of the carbamate itself in the gas. cordingly, the saturated solution passing from ,eontactor tray 2l, without consequential entrain- Acthe saturator 28 through line 33 is shown to be Vintroduced.onto .one or more .trays 3Min. the top section .of the. .conta-cion.` vwherein"` .the ...downflowing saturated solution vis .intimately .admixed v.with .the main gasstream and causedtoentrap ,any .l airline.v entrainment .or carry-over Aabove the vv.tray I2'I...Entrapment of -the entrained famine may-.occur toy some .extent by..physicalfretention in .the carbon..dioxideesaturated amine solution,

.but .mainly by reaction with.. availableecarbon dioxide in the solution to become convertedgto .thelow vapor pressurecarbamate. .I,'he.solu

tionv flowing.. .downthrougn trap, `34 isgcollected Yonthe chimney tray..35.and` returned tothe satu- .rator `-by pump 3.6-..through..-line `3'I. Aconnecting .i with. linefZS. Aportionof .thesolution` on tray 3,5 maybereturned to lthe amine.. solution stream [being reoireulated ,between the .contactorsand Still, as. by way. 'Ofiline 38. through. .which-...the carbamate solution flows. under control of=.valve 3.9. into'. the.. treating section. of..the. contacter to y be. circulated `for.-.regeneration .inthe still. v

As .previously observed. .the conversion. in .f the saturator roi Whatever amine. usecle in. .the-.plant 'treating cycle, to. v@relativelyhigh .molecular weight', low .vapor pressure compo.und.and.spe cically a carbamate. resultingfrom `thebreaction 'of the amine with carbondioxide, ,permitsrthe use inthe. lower .or treating. section the. con- Vvapor` pressures higher :thanVY the .vapor .pressure V.of monoethanolamine.v Inthegpresent system ther higher vapor. pressure amines Y:maya-be employed, with,.resl.1lt,antgreater treating efficiency `for .reasons suchrV as1 .the g-reaterintimacy' of contact made `possible 4wfitlifthe -l'e ss"viscous:amines,

by .reason ot fthe .fact that the-:vapor pressure of the carbamate '.onthe topf'trays "zZ-1'4" will ibe. sui- ...eiently `Alowl:tor avoid .any consequentialrllosses by Vaporizationfor-entrainmentr-inthe outletzgas .stream dischargedthroughy line-10. The. treated .gas is shown to be; fd-ischarged through: the iconventionalscrubber4I..

NWefclaim;

1. `rllhernethod that includes passing-,through a rst. liquid amine; solution streamfanrgaseous Stream Containing-1 anf acidic` 1 constituent. .of fthe group consisting ofi `hydrogen suliide. .and carbon dioxide V*and reactive with :the amnegithe'; gas

,leaving said solutioncontaining entrained. amine, I

contacting, and: substantiallyv saturating: acsecond $325 amine-containing s tream` with`carbon dioxide, and contacting said second fsteam'with the gas strearn after its passage" through said first `amine tream to absorbin saids'econd streananiine ntrainedinthe gas. if .i 22j The -inethod that includes passingthrough ffa'iirst liquid amine `solution':stream a gaseous treamcon-taining an acidicconstituentof the "Ugroup consisting of hydrogen sulde andfcarbon dioxide reactive With the amine, the gas leaving said solution containing entrained amine, and contacting the gas after its passage through said amineA solution stream With a liquid amine substantially saturated with carbon dioxide.

3. IThe method that includes, continuously circulating a stream of a solution containing a liquid amine through a contacting zone and a heating and regenerating zone, passing a gaseous mixture containing an acidic constituent of the group consisting of hydrogen suliide and carbon dioxide and through said contacting zone in intimate admixture with the amine solution, the gas leaving said solution containing entrained amine, passing a portion of said stream through a saturating zone and therein contacting and substantially saturating the amine solution with carbon dioxide, contacting the saturated amine solution in a second contacting zone with said gaseous mixture after its passage through said amine stream to absorb in the amine solution amine carried by the gas, and returning the amine solution from said second contacting Zone to said circulated amine stream.

4. A method that includes, continuously cirn culating a stream of a solution containing a liquid amine through a contacting zone, and a heating and regenerating Zone, passing a gaseous mixture containing hydrogen suliide and carbon dioxide through said contacting zone in intimate admixture With the amine solution for absorption of the hydrogen sulde, the gas leaving said solution containing entrained amine, passing a portion of said stream throughk a saturation zone and therein absorbing carbon dioxide in the amine solution, then contacting the solution taken from said'saturating zone and in a second contacting zone With said gaseous mixture after its passage through said amine stream to retain amine carried by the gas, and returning the amine solution from said second contacting zone to said circulated amine stream.

5. The method that includes, continuously circulating a stream of a solution containing a liquid amine having a Vapor pressure higher than the Vapor pressure of monoethanolamine through a contacting zone and a heating and regenerating zone, passing a gaseous mixture containing an acidic constituent through said contacting zone in intimate admixture With the amine solution, the gas leaving said solution containing entrained amine, passing a portion of said stream through a saturating zone and therein substantially saturating the amine solution with an acid gas, contacting the saturated amine solution in a second contacting zone with said gaseous mixture after its passage through said amine stream to re tain amine carried by the gas, and returning the amine solution from said second contacting zone to said circulated amine stream,

6. The method that includes, continuously circulating a stream of a solution containing a liquid amine having a vapor pressure higher than the vapor pressure of monoethanolamine through a contacting zone and a heating and regenerating zone, passing a gaseous mixture aanvang `v`vcontaining hydrogen sulde and carbon dioxide *through said contacting zone "in intimate admixture With the aminefsoltionfor absorption `of the `hydrogen suldepthe gas leaving said solution containing entrained amine, passing a portion of said stream through a saturation zone and therein absorbingr carbonfdioxide in the `amine solution,v then contacting the,r solution taken from said saturating Zone andzin a vsecond contacting Zone with said gaseous mixture after its passage through said amine stream to retain amine carried by the gas, and returning the amine solution from said second contacting zone to said circulated amine stream.

7. The method that includes passing a gaseous mixture containing an acidic constituent of the group consisting of hydrogen sulde and carbon dioxide through a contacting zone, passing through said zone a stream of liquid amine solution reactive with said acidic constituent, the gas leaving said solution containing entrained amine, circulating the rich amine solution from said contacting Zone to a heating and regenerating zone and returning lean solution from the heating zone to the contacting zone, passing a portion of the lean solution in a second stream through a saturating zone and therein substantially saturating the solution with carbon dioxide, contacting the gas after its passage through said amine solution in the contacting Zone with said second stream of saturated solution to entrap amine entrained in the gas, and returning at least a portion of said second stream to the first mentioned amine solution.

8. The method that includes passing a gaseous i mixture containing an acidic constituent of the group consisting of hydrogen sulfide and carbon dioxide through a contacting Zone,A passing through said zone a stream of liquid amine solution reactive with said acidic constituent, the gas leaving said solution containing entrained amine, circulating the rich amine solution from said contacting Zone to a heating and regenerating Zone and returning lean solution from the heating zone to the contacting Zone, passing a portion of the lean solution in a second stream through a saturating zone and therein substantially saturating Ythe solution with carbon dioxide, contacting the gas after its passage through said amine Vsolution in the contacting Zone with said second stream of saturated solution to entrap amine entrained inthe gas, recirculating a portion of said second stream to said saturating zone, and returning another portion of said second stream tothe nrst mentioned amine solution.

9. The method that includes passing a gaseous mixture containing an acidic constituent of the group consisting of hydrogen sulfide and carbon dioxide through a contacting zone, passing through said zone a stream of liquid amine solution reactive with said acidic constituent and having a Vapor pressure higher than the vvapor pressure of mcnoethanolamine, the gas leaving said solution containing entrained amine, circulating the rich amine solution from said contacting zone to a heating and regenerating zone and returning lean solution from the heating zone to the contacting zone, passing a portion of the lean solution in a second stream through a saturating zone and therein substantially saturating the solution with carbon dioxide, contacting the gas after its passage through said amine solution in the contacting zone with said second stream of saturated solution to entrap 

1. THE METHOD THAT INCLUDES PASSING THROUGH A FIRST LIQUID AMINE SOLUTION STREAM A GASEOUS STREAM CONTAINING AN ACIDIC CONSTITUENT OF THE GROUP CONSISTING OF HYDROGEN SULFINE AND CARBON DIOXIDE AND REACTIVE WITH THE AMINE, THE GAS LEAVING AND SOLUTION CONTAINING ENTRAINED AMINE, CONTACTING AND SUBSTANTIALLY SATURATING A SECOND AMIN-CONTAINING STREAM WITH CARBON DIOXIDE, AND CONTACTING SAID SECOND STREAM WITH THE GAS STREAM AFTER ITS PASSAGE THROUGH SAID FIRST AMINE STREAM TO ABSORD IN SAID SECOND STREAM AMINE ENTRAINED IN THE GAS. 